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(1)M. al. ay. a. EFFECT OF SPIRAL REINFORCEMENT ON AXIAL COMPRESSIVE BEHAVIOR OF TUBULAR STEEL SHORT COLUMNS FILLED WITH NORMAL AND LIGHTWEIGHT CONCRETES. U. ni. ve r. si. ty. of. MOHAMMADREZA HAMIDIAN. FACULTY OF ENGINEERING UNIVERSITY OF MALAYA KUALA LUMPUR 2018.

(2) al. ay. a. EFFECT OF SPIRAL REINFORCEMENT ON AXIAL COMPRESSIVE BEHAVIOR OF TUBULAR STEEL SHORT COLUMNS FILLED WITH NORMAL AND LIGHTWEIGHT CONCRETES. ty. of. M. MOHAMMADREZA HAMIDIAN. U. ni. ve r. si. THESIS SUBMITTED IN FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY. FACULTY OF ENGINEERING UNIVERSITY OF MALAYA KUALA LUMPUR 2018.

(3) UNIVERSITY OF MALAYA ORIGINAL LITERARY WORK DECLARATION Name of Candidate: MOHAMMADREZA HAMIDIAN Matric No: KHA110054 Name of Degree: Doctor of philosophy Title of Thesis: Effect of spiral reinforcement on axial compressive behavior of tubular steel short columns filled with normal and lightweight concretes. ay. a. Field of Study: STRUCTURAL ENGINEERING AND CONSTRUCTION I do solemnly and sincerely declare that:. ni. ve r. si. ty. of. M. al. (1) I am the sole author/writer of this Work; (2) This Work is original; (3) Any use of any work in which copyright exists was done by way of fair dealing and for permitted purposes and any excerpt or extract from, or reference to or reproduction of any copyright work has been disclosed expressly and sufficiently and the title of the Work and its authorship have been acknowledged in this Work; (4) I do not have any actual knowledge nor do I ought reasonably to know that the making of this work constitutes an infringement of any copyright work; (5) I hereby assign all and every rights in the copyright to this Work to the University of Malaya (“UM”), who henceforth shall be owner of the copyright in this Work and that any reproduction or use in any form or by any means whatsoever is prohibited without the written consent of UM having been first had and obtained; (6) I am fully aware that if in the course of making this Work I have infringed any copyright whether intentionally or otherwise, I may be subject to legal action or any other action as may be determined by UM. Date:. U. Candidate’s Signature. Subscribed and solemnly declared before, Witness’s Signature. Date:. Name: Designation:. ii.

(4) EFFECT OF SPIRAL REINFORCEMENT ON AXIAL COMPRESSIVE BEHAVIOR OF TUBULAR STEEL SHORT COLUMNS FILLED WITH NORMAL AND LIGHTWEIGHT CONCRETES. ABSTRACT Plain or reinforced concrete can be used for the concrete core in concrete filled steel tube (CFT) columns. Although CFT columns with plain concrete exhibit superior. a. performance under static and dynamic loads due to composite action, several recent. ay. studies have shown that CFT columns using reinforced concrete containing a steel cage. al. of longitudinal steel bars with hoop shaped shear reinforcement instead of plain. M. concrete provide higher strength and ductility. This is because the double confinement effect of the steel tube and steel reinforcement on the concrete core results in higher. of. strength and ductility in reinforced CFT columns (RCFT). However, ductility and the load drop percentage of RCFT columns are still considered as areas of concern. In. ty. addition, it is known that reinforced concrete columns with lateral spiral reinforcement. si. show better ductile behaviour compared to lateral hoop reinforcement, and there have. ve r. been many investigations that show the advantages of columns with spiral reinforcement. Currently, there is no investigation or literature available on CFT. ni. columns with a spirally reinforced concrete core (SRCFT) and their effect on the. U. ductility and load drop percentage. This research focuses on the effect of spiral reinforcement on the axial compressive behaviour of CFT columns with two groups of concrete – normal and lightweight – with spiral reinforcement. The results are compared with CFT columns with plain normal and lightweight concretes. The effects of different grades of normal concrete and lightweight concrete were studied on the behaviour of CFT columns with a plain and spirally reinforced concrete core. Two types of lightweight concrete, namely, oil palm shell (OPS) lightweight concrete and LECA lightweight concrete were used in this investigation. OPS concrete is known to be a iii.

(5) sustainable concrete and LECA is a well-established lightweight concrete in the construction industry. Also, the effects of spiral reinforcement characteristics, such as the pitch spacing and percentage of longitudinal steel bars, were investigated. The test results indicated that a SRCFT column has better post-yield behaviour than a CFT column for both normal and lightweight concretes. A reduction in the pitch spacing further improves the post-yield behaviour of the SRCFTs. For the lightweight concretes, spiral reinforcement improved both the strength and the ductility of SRCFT columns. ay. a. with OPS compared to CFT columns with OPS concrete. In addition, the spiral reinforcement significantly decreased the load drop percentage of the SRCFT columns. al. with LECA concrete compared to the CFT columns. Also, the use of EC4 equations. M. gives a good prediction of the test results compared to the ACI.. of. Keywords: CFT columns; RCFT columns; SRCFT columns; Spiral reinforcement;. ty. Brittle failure. U. ni. ve r. si. .. iv.

(6) KESAN TETULANG LINGKARAN PADA KELAKUAN MAMPATAN PAKSI TIUB KELULI TIANG PENDEK DIPENUHI DENGAN KONKRIT NORMAL DAN RINGAN ABSTRAK Konkrit biasa atau konkrit bertetulang boleh digunakan sebagai teras dalam tiang keluli tiub yang dipenuhi konkrit (CFT). Walaupun tiang CFT dengan konkrit biasa. a. menunjukkan prestasi unggul di bawah beban statik dan dinamik disebabkan oleh. ay. tindakan komposit, beberapa kajian baru-baru ini telah menunjukkan bahawa tiang CFT menggunakan konkrit bertetulang yang mengandungi sangkar besi bar keluli membujur. al. dengan tetulang ricih berbentuk gelung memberikan kekuatan dan kemuluran yang lebih. M. tinggi. Ini kerana kesan pengekangan dua tiub keluli dan tetulang keluli pada teras. of. konkrit menghasilkan kekuatan yang lebih tinggi dan kemuluran dalam tiang CFT bertetulang (RCFT). Walaubagaimanapun, kemuluran dan peratusan penurunan beban. ty. bagi tiang RCFT masih dianggap sebagai bidang penyelidikan yang perlu diberi. si. perhatian. Di samping itu, diketahui bahawa tiang konkrit bertetulang dengan tetulang. ve r. lingkaran sisi memperlihatkan perilaku mulur yang lebih baik berbanding tetulang gelung sisi, dan terdapat banyak penyiasatan yang menunjukkan kelebihan tiang dengan. ni. tetulang lingkaran. Pada masa ini, tiada penyiasatan atau kajian literatur bagi tiang CFT. U. dengan teras konkrit bertetulang lingkaran (SRCFT) dan kesannya terhadap kemuluran dan peratusan penurunan beban. Kajian ini menumpukan kepada kesan tetulang lingkaran pada kelakuan mampatan paksi tiang CFT dengan dua kelompok konkrit biasa dan ringan - dengan tetulang lingkaran. Hasil kajian dibandingkan dengan tiang CFT dengan konkrit biasa dan ringan. Kesan gred berbeza bagi konkrit biasa dan konkrit ringan telah dikaji pada kelakuan tiang CFT dengan teras konkrit bertetulang dan biasa. Dua jenis konkrit ringan, iaitu, konkrit ringan kelapa sawit (OPS) dan konkrit ringan LECA digunakan dalam penyiasatan ini. Konkrit OPS dikenali sebagai konkrit v.

(7) yang mampan dan LECA adalah konkrit ringan yang kukuh dalam industri pembinaan. Juga, kesan ciri tetulang lingkaran, seperti jarak dan peratusan bar keluli membujur, telah disiasat. Hasil ujian menunjukkan bahawa tiang SRCFT mempunyai kelakuan pasca alah yang lebih baik daripada tiang CFT untuk kedua-dua konkrit biasa dan ringan. Pengurangan jarak lingkaran meningkatkan lagi kelakuan pasca alah SRCFTs. Bagi konkrit ringan, tetulang lingkaran meningkatkan kedua-dua kekuatan dan kemuluran tiang SRCFT dengan konkrit OPS, berbanding dengan tiang CFT dengan. ay. a. konkrit OPS. Di samping itu, tetulang lingkaran telah menurunkan peratusan beban penurunan dengan ketara bagi tiang SRCFT dengan konkrit LECA berbanding tiang. al. CFT. Juga, penggunaan persamaan EC4 memberikan ramalan yang baik bagi keputusan. M. ujian berbanding dengan ACI.. of. Kata kunci: Tiang CFT; Tiang RCFT; Tiang SRCFT; Tetulang lingkaran; Kegagalan. U. ni. ve r. si. ty. rapuh. vi.

(8) ACKNOWLEDGEMENTS Undertaking this PhD has been a truly life-changing experience for me and it could not have been possible to do without the support and guidance that I received from others.. a. Firstly, I would like to express my sincere gratitude to my supervisors Professor Ir. Dr. Mohd Zamin bin Jumaat, Associate Prof. Dr. Ubagaram Johnson Alengaram and Associate Prof. Dr. Nor Hafizah Binti Ramli @ Sulong for the continuous support of my PhD study and related research, for their patience, motivation, and immense knowledge. Their guidance helped me in all the time of research, especially in the long time experimental researches.. ay. My sincere thanks also go to laboratory staff and those who gave access to the laboratory and research facilities. Without they precious support it would not be possible to conduct this research.. M. al. Special thanks also go to Dr. Marku Barnhardt, Dr. Walter Luiz Anrade de Oliviera, Dr. Lin-Hai Han, Dr. Shusuke Marino, DrArthur H. Nilson, Dr. Robert Park, Dr. Mohammad Shams, Dr. Alifujiang Xiamuxi, Dr. and Dr. Akira Hasegava. The results of their works played an admittedly role to set up the literature of this thesis.. U. ni. ve r. si. ty. of. Last but certainly not least, thanks to my wife, Tala, who has been by my side throughout this course, living every single minute of it. And to my darling children, Soroush and Sara for supporting me spiritually throughout my PhD study.. vii.

(9) TABLE OF CONTENTS Abstract ............................................................................................................................iii Abstrak .............................................................................................................................. v Acknowledgements ......................................................................................................... vii Table of Contents ...........................................................................................................viii List of Figures ................................................................................................................xiii. a. List of Tables.................................................................................................................. xxi. ay. List of Symbols and Abbreviations .............................................................................. xxiv. al. List of Appendices ....................................................................................................... xxvi. M. CHAPTER 1: INTRODUCTION .................................................................................. 1 Introduction.............................................................................................................. 1. 1.2. Problem statement ................................................................................................... 1. 1.3. Background .............................................................................................................. 3. 1.4. Objectives ................................................................................................................ 4. 1.5. Scope of work .......................................................................................................... 5. ty. si. ve r. Outline of the thesis ................................................................................................. 6. ni. 1.6. of. 1.1. CHAPTER 2: LITERATURE REVIEW ...................................................................... 7 Introduction.............................................................................................................. 7. 2.2. Steel-concrete Composite Structures ....................................................................... 7. 2.3. Review of past work on CFT columns .................................................................. 14. 2.4. Review of RCFT Structures .................................................................................. 20. 2.5. Pre- and post-peak Behaviour of CFT and RCFT columns ................................... 25. U. 2.1. 2.5.1. CFT columns ............................................................................................ 25. 2.5.2. RCFT columns ......................................................................................... 30. viii.

(10) 2.6. Spiral reinforcement .............................................................................................. 31. 2.7. Lightweight aggregate concrete ............................................................................. 33. 2.8. 2.7.1. Oil palm shell (OPS) lightweight aggregate............................................. 34. 2.7.2. Lightweight expanded clay aggregate (LECA) ........................................ 37. 2.7.3. OPS and LECA lightweight aggregates concrete in CFT columns .......... 38. Research Gaps ....................................................................................................... 39. ay. a. CHAPTER 3: RESEARCH METHODOLOGY ....................................................... 41 Introduction............................................................................................................ 41. 3.2. Materials ................................................................................................................ 41 Concrete.................................................................................................... 41. M. 3.2.1. al. 3.1. 3.2.1.1 Normal concrete ........................................................................ 42. 3.2.2. of. 3.2.1.2 Lightweight concrete ................................................................. 42 Steel .......................................................................................................... 44. ty. 3.2.2.1 Steel tube ................................................................................... 44. Fabrication the specimens...................................................................................... 47. ve r. 3.3. si. 3.2.2.2 Steel bar ..................................................................................... 45. 3.3.1. Specimens with normal concrete .............................................................. 47. U. ni. 3.3.1.1 CFT and SRCFT columns with normal concrete ...................... 47 3.3.1.2 Pitch spacing effect on the axial compressive behaviour of SRCFT columns ........................................................................ 55 3.3.1.3 Effect of longitudinal steel bar percentage on the axial compressive behaviour of SRCFT columns .............................. 58. 3.3.2. Specimens with OPS lightweight concrete .............................................. 61 3.3.2.1 CFT columns with OPS concrete .............................................. 61 3.3.2.2 CFT columns with different grades of OPS concrete and different diameters of steel tube ................................................ 62 ix.

(11) 3.3.2.3 SRCFT columns with OPS concrete ......................................... 64 3.3.2.4 SRCFT columns with different grades of OPS concrete ........... 65 3.3.3. Specimens with LECA lightweight concrete ........................................... 66 3.3.3.1 CFT columns with LECA concrete ........................................... 66 3.3.3.2 SRCFT with LECA concrete ..................................................... 67. TEST SETUP ........................................................................................................ 69. 3.5. Instrumentation ...................................................................................................... 70. ay. a. 3.4. CHAPTER 4: RESULTS AND DISCUSSION .......................................................... 72 Introduction............................................................................................................ 72. 4.2. Normal concrete..................................................................................................... 72 4.2.1. M. al. 4.1. CFT and SRCFT columns with normal concrete ..................................... 72. of. 4.2.1.1 CFT column specimens ............................................................. 73 4.2.1.2 SRCFT column specimens ........................................................ 80 Pitch spacing effect of spiral reinforcement on the axial compressive. ty. 4.2.2. si. behaviour of SRCFT columns .................................................................. 82. ve r. 4.2.2.1 Load-displacement curve of specimens .................................... 83 4.2.2.2 Load drop of specimens ............................................................ 83. U. ni. 4.2.2.3 Relationship between 𝝆𝒔𝒑 and percentage of load drop ........... 85 4.2.2.4 Post-yield behaviour of specimens ............................................ 88 4.2.2.5 Failure mode of specimens ........................................................ 88 4.2.2.6 Experimental test results compared to predicted values from standards .................................................................................... 91. 4.2.3. Effect of longitudinal steel bar percentage on the axial compressive behaviour of SRCFT columns .................................................................. 94 4.2.3.1 Load-displacement curve of specimens .................................... 94 4.2.3.2 Axial strength of specimens ...................................................... 95 x.

(12) 4.2.3.3 Load drop of specimens ............................................................ 95 4.3. OPS lightweight concrete ...................................................................................... 97 4.3.1. CFT columns with OPS concrete ............................................................. 97 4.3.1.1 Load-displacement curve of specimens .................................... 97 4.3.1.2 Pre-peak load behaviour of specimens ...................................... 98 4.3.1.3 Post-peak behaviour of specimens .......................................... 100 4.3.1.4 Specific energy absorption (SEA) ........................................... 101. ay. a. 4.3.1.5 Structural efficiency ................................................................ 102 4.3.1.6 Failure mode of specimens ...................................................... 103. 104. M. core. al. 4.3.1.7 The failure mechanism before the shear cracks in the concrete. 4.3.1.8 The failure mechanism after shear cracks in the concrete core. CFT columns with different grades of OPS concrete and different types of. ty. 4.3.2. of. 107. steel tube ................................................................................................. 109. si. 4.3.2.1 Load-displacement curve of specimens .................................. 109. ve r. 4.3.2.2 Failure mechanism of CFT columns with OPS concrete ........ 111. 4.3.3. SRCFT columns with OPS concrete ...................................................... 116. ni. 4.3.3.1 Load-displacement curve of specimens .................................. 117. U. 4.3.4. SRCFT columns with different grades of OPS concrete ........................ 119 4.3.4.1 Load-displacement curve of specimens .................................. 119 4.3.4.2 Effect of OPS concrete grade on the axial behaviour of SRCFT columns ................................................................................... 120. 4.4. LECA concrete .................................................................................................... 122 4.4.1. CFT columns with LECA concrete ........................................................ 123 4.4.1.1 Load-displacement curve of specimens .................................. 123. xi.

(13) 4.4.1.2 Load drop of specimens .......................................................... 124 4.4.2. SRCFT columns with LECA concrete ................................................... 125 4.4.2.1 Load-displacement curve of specimens .................................. 126 4.4.2.2 Load drop of CFT specimens with LECA concrete ................ 127 4.4.2.3 Load drop of SRCFT specimens with LECA concrete ........... 128. CHAPTER 5: CONCLUSIONS AND RECOMMENDATIONS ........................... 130. a. ay. Effect of spiral reinforced concrete core in normal concrete ................. 130. 5.1.2. Effect of pitch spacing in SRCFT with normal concrete ....................... 131. 5.1.3. Effect of the longitudinal steel bars percentage in SRCFT .................... 132. 5.1.4. CFT and SRCFT in lightweight concrete ............................................... 132. 5.1.5. Comparison of CFT and SRCFT in normal and lightweight concrete ... 133. M. al. 5.1.1. Recommendations................................................................................................ 134. ty. 5.2. Conclusions ......................................................................................................... 130. of. 5.1. ve r. si. REFERENCES………… ............................................................................................ 135. ni. LIST OF PUBLICATIONS AND PAPERS PRESENTED .................................... 144. U. APPENDIX A: FABRICATION THE SPECIMENS.............................................. 145. APPENDIX B: MATERIAL PROPERTIES (STEEL COUPON TESTING) ...... 158. APPENDIX C: LOAD-DISPLACEMENT CURVES OF SPECIMENS .............. 163. xii.

(14) LIST OF FIGURES Figure ‎2.1: Typical cross-sections of SRC and CFT composite columns and notation ("Eurocode 4.Design of composite steel and concrete structures," EN, 1994) ................. 9 Figure ‎2.2: Load deformation relation for circular CFT columns (Shams & Saadeghvaziri, 1997) ....................................................................................................... 10. a. Figure ‎2.3: Load deformation relation for square CFT columns (Shams &. ay. Saadeghvaziri, 1997) ....................................................................................................... 10. al. Figure ‎2.4: Confined effect for a circular CFT column (Morino & Tsuda, 2003) .......... 11. M. Figure ‎2.5: Lateral pressure on the steel tube and triaxial stress on the concrete core. of. (Kuranovas & Kvedaras, 2007)....................................................................................... 12. ty. Figure ‎2.6: Changes in buckling mode with length due to the presence of infill (Z. Lai,. si. Varma, & Zhang, 2014) .................................................................................................. 12. ve r. Figure ‎2.7: Different types of connection in the composite structures (Morino, 2005).. 14 Figure ‎2.8: Model and formation of CFT and RCFT columns (Xiamuxi & Hasegawa,. U. ni. 2012b) ............................................................................................................................. 21 Figure ‎2.9: Illustrations of formation of the RCFT columns (Xiamuxi & Hasegawa, 2012b) ............................................................................................................................. 24 Figure ‎2.10: Failure patterns of the selected specimen of RCFT columns (Xiamuxi & Hasegawa, 2012b) ........................................................................................................... 24 Figure ‎2.11: Typical axial stress (𝜎𝑠𝑐) versus axial strain (𝜀𝑠𝑐) curves in composite section (𝜉0=1.1 for circular CFT columns) (L.-H. Han et al., 2005) .............................. 26 xiii.

(15) Figure ‎2.12: Axial load vs. axial strain for CFT columns (de Oliveira et al., 2009) ...... 28 Figure ‎2.13: Load drop definition ................................................................................... 28 Figure ‎2.14: Load drop percentage (LD%) vs. contribution factor (ξ) of CFT column with normal concrete ....................................................................................................... 30 Figure ‎2.15: Axial compressive behaviour of tied and spiral RC columns (Nilson et al.,. ay. a. 2010) ............................................................................................................................... 32 Figure ‎2.16: Tied and spiral columns in Olive View hospital after earthquake (Park &. al. Paulay, 1975) .................................................................................................................. 32. M. Figure ‎2.17: Oil palm shell (OPS) as a waste part of the palm fruit ............................... 35. of. Figure ‎2.18: Lightweight expanded clay aggregates (LECA) ........................................ 37. ty. Figure ‎2.19: Typical load-displacement graph for a single LECA pellet under axial. si. compression test (Bernhardt et al., 2014)........................................................................ 38. ve r. Figure ‎2.20: Spirally reinforced concrete-filled steel tube (SRCFT) (Hamidian, Jumaat,. ni. Alengaram, Sulong, & Shafigh, 2016) ............................................................................ 40. U. Figure ‎3.1: Different diameter sizes of steel tubes .......................................................... 45 Figure ‎3.2: Tensile test of 6 mm steel bar in a 100 kN Instron testing machine............. 46 Figure ‎3.3: Formation of SRCFT specimens .................................................................. 50 Figure ‎3.4: Spiral steel cage ............................................................................................ 51 Figure ‎3.5: Spiral steel cage and steel tube ..................................................................... 51. xiv.

(16) Figure ‎3.6: Spiral steel cage installation ......................................................................... 52 Figure ‎3.7: SRCFT specimen after spiral installation ..................................................... 52 Figure ‎3.8: Specimens before casting ............................................................................. 53 Figure ‎3.9: Casting of specimens .................................................................................... 53. a. Figure ‎3.10: Curing of specimens ................................................................................... 54. ay. Figure ‎3.11: Specimens before and after capping ........................................................... 54. al. Figure ‎3.12: Complete spiral steel cores of different pitch ............................................. 57. M. Figure ‎3.13: Specimen before steel cage installation (15 mm clear pitch spacing) ........ 57. of. Figure ‎3.14: Spiral steel cores of different diameter of longitudinal steel bars .............. 60. ty. Figure ‎3.15: Collection of spiral steel cores with different longitudinal steel bars ........ 60. ve r. si. Figure ‎3.16: Specimen after installation in the test machine and before test .................. 69 Figure ‎3.17: Selected specimen during the testing process............................................. 70. U. ni. Figure ‎3.18: Schematic model of specimen and instrumentations .................................. 71 Figure ‎4.1: Load-displacement curves of CFT40-101 specimens .................................. 73 Figure ‎4.2: Load-displacement curves of CFT40-113 specimens .................................. 74 Figure ‎4.3: Load-displacement curves of CFT40-140 specimens .................................. 74 Figure ‎4.4: Load-displacement curves of CFT50-101 specimens .................................. 75 Figure ‎4.5: Load-displacement curves of CFT50-113 specimens .................................. 75 xv.

(17) Figure ‎4.6: Load-displacement curves of CFT50-140 specimens .................................. 76 Figure ‎4.7: Mean curves of load-displacement of CFT40 and CFT50 specimens ......... 76 Figure ‎4.8: Load drop percentage versus contribution factor for present and previous studies.............................................................................................................................. 79 Figure ‎4.9: Load drop percentage versus contribution factor for combined previous and. ay. a. present studies ................................................................................................................. 79 Figure ‎4.10: Mean curves of load-displacement of SRCFT40 and SRCFT50 specimens. al. ......................................................................................................................................... 81. M. Figure ‎4.11: Mean curves of load-displacement of CFT40 and SRCFT40 specimens ... 81. of. Figure ‎4.12: Mean curves of load-displacement of CFT50 and SRCFT50 specimens ... 82. ty. Figure ‎4.13: Mean curves of load-displacement of CFT50 and SRCFT50 specimens ... 83. ve r. si. Figure ‎4.14: Comparison of the load drop in specimens with different pitch spacing ... 85 Figure ‎4.15: Percentages of load drop in mean curves with different pitch spacing ...... 85. U. ni. Figure ‎4.16: Relationship between 𝜌𝑠𝑝 and the load drop percentage ........................... 87 Figure ‎4.17: Failure modes of specimens: 4.25a) CFT, 4.25b) SRCFT-S45, 4.25c) SRCFT-S35, 4.25d) SRCFT-S25, 4.25e) SRCFT- S15 .................................................. 90 Figure ‎4.18: Failure modes in concrete core: 4.26a) CFT specimens, 4.26b) SRCFT specimens ........................................................................................................................ 90 Figure ‎4.19: Mean curves of load-displacement of CFT50 and SRCFT50 specimens ... 95. xvi.

(18) Figure 4.20: Relationship between the percentage of longitudinal steel bars ( 𝜌𝑠𝑏) and the ultimate strength of columns (N1) ............................................................................ 96 Figure ‎4.21: Mean values of NCFT and LCFT samples ................................................. 99 Figure ‎4.22: Failure mode of specimens at the end of the test: 4.37a) NCFT-1, 4.37b) NCFT-2, 4.37d) LCFT-1, 4.37e) LCFT- ...................................................................... 103. a. Figure ‎4.23: Inside the specimens after cutting: 4.38a) NCFT specimen, 4.38b) LCFT. ay. specimen ........................................................................................................................ 104. al. Figure ‎4.24: Axial load vs. axial and lateral strain curves of NCFT specimen ............ 105. M. Figure ‎4.25: Axial load vs. axial and lateral strain curves of LCFT specimen ............. 105. of. Figure ‎4.26: The cracked surfaces: 4.41a) normal weight concrete, 4.41b) OPS. ty. lightweight concrete ...................................................................................................... 107. si. Figure ‎4.27: The samples in the two groups after testing: 4.42a) NCFT samples, 4.42b). ve r. LCFT samples ............................................................................................................... 108. ni. Figure ‎4.28: Mean curves of axial load-displacement of specimens ............................ 110. U. Figure ‎4.29: Load drop percentage versus contribution factor for OPS and normal. concrete, individually .................................................................................................... 111 Figure ‎4.30: Cracked surfaces for two types of normal and OPS concrete .................. 112 Figure ‎4.31: Schematic behaviour of granite and OPS aggregate under shear force: 4.31a) Granit aggregate, 4.31b) OPS aggregate, 4.31c) Detail A ................................. 114. xvii.

(19) Figure ‎4.32: Failure mode of the specimens after test: a) NCFT sample after cutting, b) LCFT sample after cutting, c) Removed loose crushed concrete of normal weight concrete, d) Removed loose crushed concrete of OPS concrete ................................... 116 Figure ‎4.33: Mean curves of axial load-displacement of specimens ............................ 117 Figure ‎4.34: Mean curves of axial load-displacement of specimens ............................ 120. a. Figure ‎4.35: Relationship between grade of OPS concrete and increase percentage of the. ay. strength for SRCFT columns compared to CFT columns............................................. 122. al. Figure ‎4.36: Mean curves of axial load-displacement of specimens ............................ 124. M. Figure ‎4.37: Mean curves of axial load-displacement of specimens ............................ 126. of. Figure ‎4.38: Load drop percentage (LD%) versus contribution factor (ξ) for three types. ty. of CFT columns with OPS, LECA and normal concretes ............................................ 128. si. Figure ‎4.39: Load drop percentage of CFT and SRCFT columns with LECA concrete. ve r. ....................................................................................................................................... 129. ni. Figure A.1: Complete specimens in testing room ......................................................... 145. U. Figure A.2: 150 x 300 mm cylinder samples ................................................................ 145 Figure A.3: Specimens after steel cage installation, before and after casting ............... 146 Figure A.4: Curing and capping of the specimens ........................................................ 146 Figure A.5: Completed samples in test room ................................................................ 147 Figure A.6: SRCFT specimens before casting in third group ....................................... 148. xviii.

(20) Figure A.7: SRCFT specimens after casting in third group .......................................... 148 Figure A.8: Curing the samples in third group ............................................................. 149 Figure A.9: Specimens after capping in third group ..................................................... 149 Figure A.10: Steel tubes before casting ........................................................................ 150. a. Figure A.11: Steel tubes after casting ........................................................................... 150. ay. Figure A.12: Curing of specimens ................................................................................ 151. al. Figure A.13: Specimens after capping and before test ................................................. 151. M. Figure A.14: Number of specimens with different diameters before casting ............... 152. of. Figure A.15: Number of samples with different diameters after casting ...................... 152. ty. Figure A.16: Two different diameter sizes of complete samples before capping ......... 153. ve r. si. Figure A.17: Two different diameter sizes of complete samples after capping............ 153 Figure A.18: CFT and SRCFT specimens before casting ............................................. 154. U. ni. Figure A.19: CFT and SRCFT samples after casting ................................................... 154 Figure A.20: Specimens before casting ........................................................................ 155 Figure A.21: Specimens after casting ........................................................................... 155 Figure A.22: Specimens before casting ........................................................................ 156 Figure A.23: Specimens after casting ........................................................................... 156 Figure A.24: Specimens after casting ........................................................................... 157 xix.

(21) Figure C.‎1: Load-displacement curves of SRCFT40 specimens .................................. 163. U. ni. ve r. si. ty. of. M. al. ay. a. Figure C.2: Load-displacement curves of SRCFT50 specimens .................................. 163. xx.

(22) LIST OF TABLES Table ‎2.1: Summary of past work on CFT columns ....................................................... 19 Table ‎2.2: Specification of SRCFT specimens with lateral hoop reinforcement ............ 23 Table ‎2.3: Relationship between the contribution factor (ξ) and the load drop percentage. a. (LD%) of CFT columns .................................................................................................. 29. ay. Table ‎3.1: Mix proportions of two types of normal concrete ......................................... 42. al. Table ‎3.2: Mix proportions of three grades of OPS concrete ......................................... 43. M. Table ‎3.3: Mix proportions of three grades of LECA concrete ...................................... 43. of. Table ‎3.4: Specification of steel tubes ............................................................................ 44. ty. Table ‎3.5: Specifications of steel bars (mild steel) ......................................................... 46. si. Table ‎3.6: CFT specimens in the first group ................................................................... 48. ve r. Table ‎3.7: SRCFT specimens in the first group .............................................................. 49. ni. Table ‎3.8: Specification of CFT and SRCFT specimens in second group...................... 56. U. Table ‎3.9: Specification of CFT and SRCFT specimens in third group ......................... 59 Table ‎3.10: Mix proportions of grade 55 of normal concrete ......................................... 61 Table ‎3.11: Specifications of the fourth group of specimens.......................................... 62 Table ‎3.12: Specification of specimens in fifth group .................................................... 63 Table ‎3.13: Specification of CFT and SRCFT specimens in sixth group ....................... 64. xxi.

(23) Table ‎3.14: Specification of CFT samples ...................................................................... 65 Table ‎3.15: Specification of SRCFT samples ................................................................. 66 Table ‎3.16: Mix proportions of normal concrete with grade 30 ..................................... 67 Table ‎3.17: Specification of the specimens in eighth group ........................................... 67. a. Table ‎3.18: Specification of CFT samples ...................................................................... 68. ay. Table ‎3.19: Specification of SRCFT samples ................................................................. 68. al. Table ‎4.1: Contribution factor and load drop percentage for CFT in the first group of. M. specimens ........................................................................................................................ 78. of. Table ‎4.2: Results of experimental tests for different condition of columns .................. 84. ty. Table ‎4.3: Comparison of test results with EC4 and ACI for CFT and SRCFT specimens. si. with normal concrete ....................................................................................................... 93. ve r. Table ‎4.4: Effect of cross-sectional area of longitudinal bars (𝐴𝑠𝑏) on the axial strength of specimens .................................................................................................................... 96. U. ni. Table ‎4.5: Experimental tests results for CFT and SRCFT columns .............................. 97 Table ‎4.6: Load and corresponding displacement values of the NCFT and LCFT specimens ........................................................................................................................ 99 Table ‎4.7: Energy absorption and specific energy absorption of specimens ................ 102 Table ‎4.8: Structural efficiency of two groups of specimens ....................................... 102. xxii.

(24) Table ‎4.9: Contribution factor and load drop percentage for CFT specimens with OPS concrete ......................................................................................................................... 110 Table ‎4.10: Load drop percentage of specimens ........................................................... 118 Table ‎4.11: Load drop percentage for mean value of specimens .................................. 119 Table ‎4.12: Load drop percentage of specimens ........................................................... 121. ay. a. Table ‎4.13: Load drop percentage for mean value of specimens .................................. 122. al. Table ‎4.14: Load drop percentage of specimens ........................................................... 125. M. Table ‎4.15: Load drop percentage for mean value of specimens .................................. 125. of. Table ‎4.16: Contribution factor and load drop percentage for SRCFT specimens with. ty. LECA concrete .............................................................................................................. 128. si. Table B.1: Size of Rectangular Tension Test Specimens ............................................. 158. U. ni. ve r. Table B.2: Size of Round Tension Test Specimen ....................................................... 159. xxiii.

(25) LIST OF SYMBOLS AND ABBREVIATIONS :. Cross-section area of concrete core. 𝐴𝑔. :. Cross-sectional area of composite column. 𝐴𝑠𝑏. :. Cross-sectional area of longitudinal steel bars. 𝐴𝑠𝑝. :. Cross-sectional area of spiral steel bars. 𝐴𝑠𝑡. :. Cross-section area of steel tube. CFT. :. Concrete filled steel tube. 𝑑𝑏. :. Diameter of longitudinal steel bar. 𝑑𝑝. :. Diameter of spiral steel bar. D. :. Diameter of steel tube. 𝐷𝑝. :. Diameter of spiral core concrete. 𝐸𝑎. :. Modulus of elasticity of steel tube. 𝐸𝑠. :. Modulus of elasticity of steel bar. 𝐸𝑐𝑚. :. Secant modulus of elasticity of concrete. 𝑓𝑐𝑘. :. Characteristic concrete strength (𝑓𝑐𝑘 = 0.67𝑓𝑐𝑢 ). 𝑓𝑐𝑢. :. Concrete cube strength. :. Yield stress of longitudinal steel bar. :. Yield stress of spiral steel bar. 𝑓𝑦𝑡. :. Yield stress of steel tube. 𝑓𝑐′. :. Compressive strength of standard cylinder. 𝐼𝑎. :. Second moment of area of the steel tube. 𝐼𝑐. :. Second moment of area of the un-cracked concrete section. 𝐼𝑠. :. Second moment of area of the steel bar. L. :. Length of specimen. n. :. Number of longitudinal steel bars. U. ay. al M. of. ty. si. ni. 𝑓𝑦𝑝. ve r. 𝑓𝑦𝑏. a. 𝐴𝑐. xxiv.

(26) N. :. Axial Load. N1. :. Maximum axial strength of specimen. N2. :. Minimum axial strength of specimen after load drop. 𝑁𝑒𝑥𝑝. :. Experimental ultimate strength. 𝑁𝑅. :. Residual load. Reinforced concrete filled steel tube. s. Center to center spacing of spiral. :. ay. RCFT :. a. 𝑃𝑛,𝑚𝑎𝑥 : Maximum allowable value of nominal axial strength of cross section. Spirally reinforced concrete filled steel tube. t. :. Wall thickness of steel tube. 𝑈. :. Displacement. 𝑈1. :. Displacement corresponding to maximum axial load. 𝑈2. :. Displacement corresponding to minimum axial load after load drop. 𝑈𝑅. :. Displacement corresponding to residual load (𝑁𝑅 ). 𝜌𝑠𝑏. :. Ratio of 𝐴𝑠𝑏 to 𝐴𝑔. 𝜌𝑠𝑝. : Ratio of volume of spiral reinforcement to total volume of core confined by the spiral. M. of. ty. si. ve r :. Ratio of 𝐴𝑠𝑡 to 𝐴𝑔. U. ni. 𝜌𝑠𝑡. al. SRCFT:. xxv.

(27) LIST OF APPENDICES 152. Appendix B: Material properties (steel coupon testing)……………………….. 165. Appendix C: Load-displacement curves of specimens…………………………. 170. U. ni. ve r. si. ty. of. M. al. ay. a. Appendix A: Fabrication the specimens...............................………………….... xxvi.

(28) CHAPTER 1: INTRODUCTION 1.1. Introduction. Concrete filled steel tube (CFT) columns have been widely used in the construction industry because of their superior structural behaviour, such as high strength and ductility. The mechanical properties of both the concrete core and the steel tube in the CFT columns significantly improve due to the composite action. The enhancement of the strength and ductility of the CFT columns depends on several factors, such as the. ay. a. strength of the concrete, and the thickness and shape of the steel tube. In the past, many investigations have been conducted on different methods of construction of CFT. al. columns to improve their features. Considering the rapid increase in the usage of this. M. group of columns in different types of structure, such as high-rise buildings, bridges and piles, more investigations are required to ascertain the significant factors that could. of. influence the behaviour of the CFT columns in order to use them in more effective. ty. ways. Problem statement. si. 1.2. ve r. Steel tube and concrete are the main materials of composite columns. The compressive strength of concrete is substantial compared to its tensile strength;. ni. however, due to its brittle behaviour, concrete suffers sudden failure in compression.. U. After the maximum compression load, the sudden drop in its load-displacement curve is testament to the brittle behaviour of concrete. In contrast, although steel is known for its ductility and high strength, it mostly shows a sharp drop after the peak-load in the loaddisplacement curve. This is due to the local buckling of the steel tube in compression; furthermore, thinner steel tubes experience a higher load drop after the maximum load. In comparison to concrete and steel tube as individual entities, composite columns provide better performance due to the better mechanical properties of the concrete core and the steel tube. This is largely attributable to the two reasons given below: 1.

(29) i.. The concrete core provides lateral support for the steel tube and delays the local buckling.. ii.. Surrounding the concrete core with steel tube increases its triaxial stress, and, consequently, the strength and ductility of the concrete core improve.. The improvements of the materials are evidenced in the load-displacement curve of CFT columns by their higher strength and ductility; furthermore, this curve can show. a. different load drop percentages after the peak-load depending on the characteristics of. ay. the concrete core and steel tube.. al. The load drop percentage in the CFT columns forms the post-peak stage, which is. M. considered to be one of the most important features of composite columns. The postpeak behaviour shows the main structural properties of columns, such as ductility,. of. energy absorption, and failure mode. The simplest method to improve the post-peak. ty. behaviour of CFT columns is by providing a steel tube of greater thickness; a thicker steel tube has a higher confinement effect on the concrete core and results in higher. si. triaxial stress, and, consequently, the higher strength and ductility of composite. ve r. columns. Considering the importance of the performance of the concrete core on the behaviour of composite columns, in recent years, researchers have investigated new. U. ni. methods to improve the performance of concrete in CFT columns. In addition, the large self-weight of normal concrete increases the size of the. structural members, and, consequently, the cost of the foundation in reinforced concrete and composite structures. In recent years, the use of lightweight concrete instead of normal concrete has been extensively investigated. In recent years, many studies were being conducted on the CFT columns to investigate the performance of the composite columns in terms of strength and ductility.. 2.

(30) In 2012, Xiamuxi et al. replaced the plain concrete core with a reinforced concrete core and showed that the reinforced concrete filled steel tube (RCFT) columns exhibited better structural behaviour compared to plain concrete. They used a steel cage of longitudinal steel bars with hoop shaped shear reinforcement and showed that RCFT columns provide better strength and ductility compared to CFT columns. However, it is known that reinforced concrete columns with lateral spiral reinforcement show much better ductile behaviour compared to hoop shear reinforcement. Although the use of. ay. a. spiral links in RCFT could enhance the strength and ductility behaviour of RCFT columns, there has been no investigation or literature available on lateral spiral. al. reinforcement in RCFT columns. Hence, in this study, the effect of spirally reinforced. M. concrete filled steel tube (SRCFT) columns is investigated. Background. of. 1.3. Although in recent years, the studies of CFT columns have had a significant. ty. breakthrough in terms of research and development, these types of column are not new. si. and have been known for a long period of time. CFT columns were first used in Great. ve r. Britain during the late 1890s in the construction of road bridges. However, the early 1900s are considered to be an important starting point in the experimental and analytical. ni. investigation of composite columns when they were used in the construction of a. U. number of buildings and bridges. In the United States, the first documented design concept of CFT columns was presented by Swain and Holmes in 1915; from then on, until 1932, more than 1500 tests were conducted on composite columns in North America and Europe. Based on the previous studies conducted, in 1924, the American “Standard Specifications for Concrete and Reinforced Concrete” was published, which gave explicit formulas for composite columns. This standard was used for the construction of. 3.

(31) tall buildings in Chicago during the 1920s and 1930s. After a period of oblivion due to World War II, the investigation of CFT columns was intensified from 1950, and many analytical and experimental studies were conducted in different countries. The results of investigations showed the superior advantages of CFT columns for seismic-resistant structures, high-rise buildings, bridge piers, and piles. CFT columns provide substantial energy dissipation under seismic load and composite frames have been shown to. a. provide great monotonic and seismic resistance behaviour in two orthogonal directions.. ay. In recent years, many investigations have studied the use of lightweight concrete to. al. decrease the total weight of reinforced concrete and composite structures. Thus, as highlighted before, in order to reduce the self-weight of normal weight concrete, the. M. utilization of locally available lightweight aggregates in the development of lightweight The lower. of. concrete in CFT and SRCFT columns is considered in this investigation.. weight of structures has a significant effect on the final cost and also the performance of. Objectives. si. 1.4. ty. buildings, especially against dynamic loads.. ve r. In this study, two types of concrete – normal weight and lightweight – were used in the steel tube. Normal weight concrete filled steel tube (NCFT) circular columns and. ni. lightweight concrete filled steel tube (LCFT) circular columns were investigated for. U. plain and reinforced concrete. For both types of concrete, the behaviour of CFT columns was studied for different variables – different grades and types of concrete, thickness and diameter of steel tube, pitch spacing of spiral links, and different percentages of longitudinal reinforcement.. 4.

(32) The objectives of the present study are described as outlined below: i.. To investigate the axial compressive behaviour of normal concrete filled steel tube (NCFT) columns with and without spiral reinforcement.. ii.. To examine the pitch spacing effect of spiral reinforcement on the axial compressive behaviour of NCFT columns.. iii.. To examine the effect of the longitudinal bars percentage on the axial compressive. To investigate the axial compressive behaviour of lightweight concrete filled steel. ay. iv.. a. behaviour of NCFT columns.. and without spiral reinforcement.. To compare the behaviour of CFT and SRCFT columns using OPS, LECA and. M. v.. al. tube (LCFT) columns using oil palm shell (OPS) and LECA as aggregate with. Scope of work. ty. 1.5. of. normal weight concrete, especially in the case of the post-peak stage.. CFT columns have been increasingly used in different structures. Considering the. si. wide usage of this group of columns in the construction industry, the efficiency of CFT. ve r. columns is vital. The scope of this study is to investigate the axial compressive behaviour of the circular composite columns using plain and reinforced concrete with. ni. normal weight, and lightweight aggregate concretes. Many studies have been conducted. U. using different types of CFT column to investigate better structural behaviour and efficiency. In this study, new specifications for composite columns were utilised to achieve higher performance of CFT columns. For this purpose, the new composite columns using two types of lightweight concrete with OPS and LECA as lightweight aggregates, and normal weight concrete were prepared and tested. Then, based on the experimental results, the new types of composite columns were proposed with normal and lightweight 5.

(33) concretes. The concrete core for both normal and lightweight concretes was investigated for plain and spirally reinforced concrete cores. To study the effect of the concrete grade, three different grades of normal concrete (C30, C40, and C50), OPS lightweight concrete (C20, C30, and C40) and LECA lightweight concrete (C15, C20, C30) were used to manufacture the CFT columns with and without spiral reinforcement. Also, to investigate the effect of the spiral reinforcement characteristics on the axial. a. compressive behaviour of CFT columns, different percentages of spiral links and. ay. longitudinal steel bars were used to make the CFT columns. For this aim, in fabricating. al. the CFT columns, the spiral steel cage was prepared with spiral links at different pitch spacing and different diameters of longitudinal steel bars. In addition, to study the effect. M. of the steel tube specifications, different thicknesses and diameters of the steel tubes. Outline of the thesis. ty. 1.6. of. were used to manufacture the CFT columns with plain and spirally reinforced concrete.. The review on the existing CFT columns with different types of steel tube and. si. concrete core is outlined in chapter 2. Furthermore, the behaviour of CFT columns. ve r. using plain and reinforced concretes and their properties is also reviewed in this chapter.. ni. Also, the lightweight concrete filled steel tube column is reviewed.. U. Chapter 3 describes the fabrication of the specimens, test setup, and instrumentation. for experiments. Chapter 4 presents the experimental results for the specimens. A comparison between the test results in the different types of specimens is explicitly done to identify the specific properties of each group. Finally, Chapter 5 summarizes the findings of the research and several recommendations for future works are suggested. 6.

(34) CHAPTER 2: LITERATURE REVIEW 2.1. Introduction. A review of the history of composite columns as a basic structural member of composite structures is presented. The benefits of this group of columns are presented, and the different types of composite column are briefly introduced. In addition, a review of the concrete filled steel tube (CFT) columns as the most popular composite column is provided. The core of CFT columns can be plain or reinforced concrete. A review of. ay. a. reinforced concrete filled steel tube (RCFT) columns and their specifications are also. 2.2. Steel-concrete Composite Structures. al. presented.. M. Based on the materials used, conventional structural systems may be characterized. Wood structures: light, energy saving and beautiful, but short life, flammable, not. ty. i.. of. as:. suitable for constructing high-rise buildings and poor resistance to corrosion. Masonry structures: cheap to construct, but very poor resistance to earthquakes.. iii.. Reinforced concrete (RC) structures: main structural system, cheap compared to. ve r. si. ii.. steel structures and long-life, but heavy. Steel structures: fast to construct, good for earthquake zones and suitable for large. ni. iv.. U. and high-rise buildings, but expensive to construct and maintain; they can buckle easily.. From the viewpoint of performance (especially the anti-seismic capacity) and construction cost, these structures cannot satisfy the increasing demands of construction works, such as large scale, high strength, high ductility, better anti-seismic capacity, and reasonable construction cost. Under such circumstances, researchers have constantly sought a structural system that has better ductility and anti-seismic capacity, like steel. 7.

(35) structures, and long-life like RC structures with reasonable maintenance cost. As a result, a new structural system – steel and concrete composite structures (composite structures) – has been developed. Composite structures have acquired their better performance by combining two kinds of structure or material that are totally different. Although the two different structures do not display excellent characteristics when used in isolation, when combined they. a. provide greater strength, higher ductility and better anti-seismic capacity (Endo, Shioi,. al. structural system that should be developed further.. ay. Hasegawa, & Wang, 2000). Therefore, composite structures are regarded as a good. M. Until now, most popular composite structures are mainly the Steel Reinforced Concrete (SRC) structures, and Concrete Filled Tubular steel (CFT) structures. CFT. of. structures have gained increased popularity as a column system in supporting heavy. ty. loads in high-rise and large-span constructions, bridges and offshore structures due to their excellent seismic event resistant structural properties, such as high strength, high. si. ductility, and large energy absorption capacity. Figure ‎2.1 shows the typical cross-. ve r. sections of SRC (Figures 2.1a, 2.1b, 2.1c) and CFT (Figures 2.1d, 2.1e, 2.1f) composite columns and notation in Eurocode 4 ("Eurocode 4.Design of composite steel and. U. ni. concrete structures," EN, 1994).. 8.

(36) a ay al M. of. Figure ‎2.1: Typical cross-sections of SRC and CFT composite columns and notation ("Eurocode 4.Design of composite steel and concrete structures," EN, 1994). ty. Although the square and circular cross-sectional shapes of steel tube are the most. si. favoured shapes of CFT columns, there are some significant differences in the structural. ve r. behaviour of these two types of CFT column. For instance, a confining effect can be expected for circular columns, while, for square columns, there is no increase in the. ni. axial strength due to triaxial effects despite the small slenderness ratio and large wall. U. thickness. The load-deformation behaviour of the columns is also remarkably affected by the cross-sectional shape, diameter to wall thickness ratio, and concrete strength. The load deformation relation for circular and octagonal columns shows strain hardening or an elastic-perfectly plastic behaviour (Figure 2.2), while, for all square columns, the load-deformation curve is of a degrading type.. 9.

(37) a ay al. U. ni. ve r. si. ty. of. M. Figure ‎2.2: Load deformation relation for circular CFT columns (Shams & Saadeghvaziri, 1997). Figure ‎2.3: Load deformation relation for square CFT columns (Shams & Saadeghvaziri, 1997). 10.

(38) CFT columns have several considerable advantages compared to steel and reinforced concrete columns. The orientation of the steel and concrete in the cross-section optimizes the strength and stiffness of the composite section. The steel lies at the outer perimeter where it performs most effectively in tension and in resisting bending moments. Also, the stiffness of the CFT is greatly enhanced because the steel, which has a much greater modulus of elasticity than the concrete, is situated furthest from the. a. centroid, where it makes the greatest contribution to the moment of inertia.. ay. The confined concrete created by the steel tube enhances the concrete core properties. al. by placing the concrete in triaxial stress, while the local buckling of the steel tube is delayed by the lateral pressure of the concrete core (Figure 2.5). When the failure mode. M. of CFT columns is compared with an empty steel tube, the local buckling in the CFT. of. column occurs in a different mode. The concrete prevents the steel tube from buckling inward; instead, it forces the tube to buckle in an outward mode as shown in Figure 2.6.. ty. Hence, the strength and ductility of the composite column increase significantly (Shams. U. ni. ve r. si. & Saadeghvaziri, 1997).. CFT column. Steel tube. Concrete core. Figure ‎2.4: Confined effect for a circular CFT column (Morino & Tsuda, 2003). 11.

(39) a. Concrete core element. ay. Steel tube element. ni. ve r. si. ty. of. M. al. Figure ‎2.5: Lateral pressure on the steel tube and triaxial stress on the concrete core (Kuranovas & Kvedaras, 2007). U. Figure ‎2.6: Changes in buckling mode with length due to the presence of infill (Z. Lai, Varma, & Zhang, 2014). Therefore, it is most advantageous to use CFTs for columns subjected to large. compressive loading. In contrast to reinforced concrete columns with transverse reinforcement, the steel tube also prevents spalling of the concrete and minimizes congestion of the reinforcement in the connection region, particularly for seismic design.. 12.

(40) In addition, cost savings for formwork and faster construction are other advantages of this kind of column. In moderate- to high-rise construction, the building can ascend more quickly than a comparable reinforced concrete structure since the steelwork can precede the concrete by several storeys. When compared to steel moment resisting frames, in unbraced CFT frames, the amount of savings in steel tends to grow as the number of storeys increases (Morino et al., 1996).. a. The behaviour of the connections in composite structures also shows notable. ay. advantages. Figure 2.7 shows the different types of connection in composite structures.. al. In this group of connections, the steel tube and concrete act together to provide natural reinforcement for the panel zone, which reduces the material and labour costs of the. M. connections. In addition, the smaller and lighter framework places less load on the. of. foundation, thereby introducing further cost savings. These advantages have secured an. U. ni. ve r. si. ty. expanding role for this versatile structural element in modern construction.. 13.

(41) a ay al M of ty si ve r ni. Figure ‎2.7: Different types of connection in the composite structures (Morino, 2005). U. 2.3. Review of past work on CFT columns. Various analytical and experimental studies have shown the advantages of CFT. columns. In 1957, Klöppel and Goder carried out collapse load tests on CFT columns and proposed a design formula for CFTs (Gourley, Tort, Denavit, Schiller, & Hajjar, 2008). Gardner and Jacobson attempted to predict the ultimate load of CFT columns (Gardner & Jacobson, 1967a). Furlong investigated the behaviour of CFT columns in detail and pointed out the properties of CFTs (Furlong, 1967, 1968). He presented. 14.

(42) design graphs and formulas for CFT columns. In 1970, Knowles and Park investigated axially loaded CFT columns with a wide range of slenderness ratios (Knowles & Park, 1969, 1970). They presented the design equations to compute the ultimate compression strength of CFT columns. To meet the rapidly increasing demands, a five-year research project on CFTs was carried out as part of the fifth phase of the US-Japan Cooperative Earthquake Research. a. Programme on Composite and Hybrid Structures from the fiscal year of 1993, which is. ay. perhaps regarded as the most representative one in terms of explaining the mechanical. al. properties of a CFT column system (Nishiyama & Morino, 2002). In this research project, experimental studies consisting of centrally-loaded stub columns, eccentrically-. M. loaded stub columns, beam-columns, and beam-column connections were conducted. of. (Nishiyama & Morino, 2002). A total of 154 specimens were tested. The main feature of this test programme was that it covered high-strength materials, such as 800MPa steel. ty. and 90MPa concrete. It also covered large width-to-thickness (D/t) ratios, and some of. si. the beam-column specimens were tested under varying axial loads. In addition to this. ve r. organized programme, numerous specimens of CFT members and frames have been tested in research projects in universities and industries, and a large number of technical. ni. papers have been presented at the annual meetings of the Architectural Institute of Japan. U. (AIJ). The research topics covered in the aforementioned projects are summarized as follows: i.. structural mechanics including the stiffness, strength, post-local buckling behaviour, confinement effects, stress transfer mechanisms, and the ductility of columns, beam-columns, and beam-column connections;. ii.. construction efficiency including concrete compaction, mixture, casting method and construction time;. 15.

(43) iii.. fire resistance including strength under fire and the amount of fireproof material; and. iv.. structural planning, including applications for high-rise and large-span buildings, and cost performance.. The results of these research projects have contributed greatly to improving the design and construction methods of CFTs. According to the study results, until now. a. (Amano et al., 1998; Fujimoto, Mukai, & Nishiyama, 1997; Huang et al., 2002; Jialin,. ay. HINO, & KURODA, 1996; Jiaru, Gang, Zuozhou, & Zhao, 2004; Matsui, 1994;. al. Nishiyama & Morino, 2002; Stephen P Schneider, Kramer, & Sarkkinen, 2004; Xiao,. may be summarized as follows:. Local buckling of the steel tube is delayed, and the degradation in strength after. of. i.. M. He, Mao, Choi, & Zhu, 2003; Zeghiche & Chaoui, 2005), the main advantages of CFTs. ii.. ty. the local buckling is moderated due to the restraining effect of the concrete. The concrete core is under a three-dimensional stress condition due to the lateral. si. confining pressure provided by the steel tube and diaphragms, and this lateral. ve r. confining pressure contributes to an increase in the compressive strength and ductility of the concrete core. Moreover, the steel tube prevents the concrete from. ni. peeling off and contributes to a smaller degradation in strength. Meanwhile, the. U. drying shrinkage and creep of the concrete are much smaller than that for ordinary RC.. iii.. CFT enables high-strength steel and concrete to be utilized effectively, and, hence, the size of the cross-section is reduced. This contributes to the enlargement of the effective space in buildings.. iv.. In respect of the beam-column joints, the shear-strength of the diaphragm panels can be increased even with the smaller size than usual due to the restraining effect. 16.

(44) of the concrete core. In other words, the size of the diaphragms can be reduced without decreasing the shear-strength. Fire resistance is improved as far as the thermal capacity of the filled concrete is. v.. concerned; hence, the fireproof material can be reduced or omitted. vi.. A concrete mould is unnecessary; hence, the CFT possesses excellent workability, such as saving labour and shortening the time for the works. Because of the merits above, better economic performance is obtained with CFT. ay. structures compared to that of pure steel structures.. a. vii.. al. In recent years, researchers have paid more attention to the advantages of the usage of CFT columns in the construction industry. Investigations show that CFT columns. M. provide substantial energy dissipation under seismic load, and, as a composite column. of. in composite frames, they can show considerable seismic resistance behaviour (Hajjar, 2000, 2002). The characteristics of CFT columns form a practical structural system,. ty. especially for high-rise buildings because of the higher construction efficiency (Morino. si. & Tsuda, 2002). Uchikoshi et al. (Uchikoshi, Hayashi, & Morino, 2000) through a trial. ve r. design of unbraced frames showed that the total steel consumption of the CFT system is 10% less than a steel system for the entire building.. ni. However, CFT structures still have some weak points in spite of the advantages. U. above: i.. The shear-failure of CFT structure is of concern, especially for large-scaled structures.. ii.. The ductility of CFT structures decreases with the in-filling of high-strength concrete despite the increase in strength.. iii.. There is no simple and effective way to ascertain the compactness of the in-filled concrete, especially at the joints with diaphragms. 17.

(45) Table 2.1 shows a summary of the past work on CFT columns. As can be seen in this table, many variables have been investigated in studying the behaviour of CFT columns. The effect on the behaviour of CFT columns of different parameters, such as concrete grade, wall thickness of steel tube, length of CFT column, compressive strength of concrete core, and yield strength of steel tube, have been studied. Based on the obtained results, researchers have proposed theoretical relationships to explain the behaviour of CFT columns. However, past work on CFT columns has not considered certain. U. ni. ve r. si. ty. of. M. al. lightweight concrete and reinforced concrete core.. ay. a. important objectives. For instance, there are only a few studies on CFT columns with a. 18.

(46) Table ‎2.1: Summary of past work on CFT columns. Researchers. Number of Tests. (Kloppel & Goder, 1957). 104. (Cai, 1991). U. (Kilpatrick & Rangan, 1997) (Stephen P. Schneider, 1998) (L. Han & Yan, 2000) (Johansson & Gylltoft, 2002) (Ghannam, Jawad, & Hunaiti, 2004). (Giakoumelis & Lam, 2004). 264-395. 20-29. Normal. 8602310. 20-43. Normal. 18. 127, 139.7, 168.27. 1.62-9.75. 172-278. 3183. Normal. 14. 114.3. 2.99, 4.49, 5. 279-362. 30. 158.751019.81. 5.08-13.2. 27. 165.1. 26. 190.75, 267.46. ay 17, 34. 291-391. 152, 203, 241, 304, 609, 1050, 1524, 1676 1409, 1714, 2032; 3327. a. 363-633. Normal. 252. 15-45. Normal. 477-3060. 5. 277-313. 34, 51. Normal. 665-2989. 5.99, 7.01. 505, 460. 55, 48. Normal. 1150-4572. 165.1. 0, 4.49, 5. 418, 440. 27. Normal. 1000(1 m). 173.99, 177.8, 179.83. 2.99, 5.51, 8.99. 248, 266, 283. 22, 23, 43, 45. Normal. 360. 9. 101.6. 1.60. 217. 67. Normal. 8072321. 2. 248.92. 2. 259. 59. Normal. 749. 44. 60.45, 101.6. 1.09-5.43. 308-421. 30, 46. Normal. 254, 325, 858, 1811. 24. 101.6. 2.38. 410. 95. Normal. 2174. 14. 139.95. 2.99-7.46. 284-537. 23, 30. Normal. 560-670. 11. 107.95. 4.49. 348. 31, 48. Normal. 3510-4157. 9. 158.75. 4.8. 432. 64. Normal. 650. 36. 165.1 109.98. 1.9-5. 239-366. Normal Lightweight. 2000-2500. 13. 114.06. 3.75-5.02. 342-364. Normal. 299. si. ni. (Kawano, 1997). Length of column (mm). 1.70-4.92. 4. (Rangan & Joyce, 1992) (Bridge & Webb, 1992). Concrete type. 32. 7. ve r. (Sakino & Hayashi, 1991). 𝑓𝑐′ (MPa). 76.2, 101.6, 120.65, 152.4. ty. (Masuo, Adachi, Kawabata, Kobayashi, & Konishi, 1991) (Nakai, Kurita, & Ichinose, 1991). 𝑓𝑦𝑡 (MPa). al. (Toshiyuki Kitada, Yoshida, & Nakai, 1987) (Luksha & Nesterovich, 1991). 2-11.98. Main Test variables. M. (Neogi, 1969). Wall thickness (mm). of. (Gardner & Jacobson, 1967b). Tube diameter (mm) 95.25, 120.65, 215.9. 31104. 19.

(47) Considering the great performance of CFT columns, this type of column has been widely used for seismic-resistant structures, columns in high-rise buildings, bridge piers, storage tank columns and piles (Abed, AlHamaydeh, & Abdalla, 2013; Chacón, Mirambell, & Real, 2013; Denavit & Hajjar, 2011; Dundu, 2012; Evirgen, Tuncan, & Taskin, 2014; Roeder & Lehman, 2012; Stephen P. Schneider, 1998; Shanmugam & Lakshmi, 2001; Tort & Hajjar, 2008). Due to the specification of CFT columns, recently, in the United States, CFT columns have been used as super columns for. ay. a. primary load bearing members in high-rise structures. They have provied both gravity and lateral resistance systems for the buildings (Hajjar, 2002). Kitada (T. Kitada, 1998). al. studied the properties of different types of bridge pier in Japan. The results showed that,. M. in general, the strength and ductility of composite columns are larger than that of other types, such as reinforced concrete and steel columns, while, the circular CFT columns. of. have better performance compared to other types of composite column. CFT piles can. ty. be constructed without formwork and shoring, which results in faster and more. si. economical construction (Lehman & Roeder, 2012).. ve r. CFT columns are commonly used as piers and arch ribs of bridge structures throughout Japan and China (Chen & Wang, 2009; T. Kitada, 1998). Review of RCFT Structures. ni. 2.4. U. In the Hanshin-Awaji earthquake in Japan on 17 January 1995, the CFT structures. avoided collapse whereas most of RC and steel structures were heavily damaged due to shear-failure and local buckling (Xiamuxi & Hasegawa, 2012b). As a reinforcement method, steel plates were wrapped around the RC columns, and the RC was poured into the steel tubes. These reinforced structures can be considered as the embryonic form of Reinforced Concrete Filled Tubular steel (RCFT) structures. Figure 2.8 illustrates the model and formation of CFT and RCFT columns.. 20.

(48) ay. a. Figure ‎2.8: Model and formation of CFT and RCFT columns (Xiamuxi & Hasegawa, 2012b) RCFT structures started to develop in 2000 (Endo et al., 2000; Tanigaki, Kanai, &. al. Komuro, 2002; Wang, Ishibashi, Wei, & Hasegawa, 2002). In 2001, five years after the. M. Hanshin-Awaji earthquake, their first application was with 80 MPa high strength concrete filled main columns of 102.2 m, in a 30-storey high-rise hotel building in. ty. their practical utilization.. of. Tokyo Japan. Since then, RCFT structures have developed and been studied in terms of. si. The main purpose of developing RCFT is to combine the merits of RC and CFT. ve r. structures. Although CFT structures have been proven to provide better structural performance than bare steel tube or bare RC, the brittle-failure of CFT structures is still. ni. a concern, especially when considered for the construction of large-scale structures, and. U. the ductility is also of concern when high strength concrete is used. To improve these shortcomings of CFT, a better way might be to insert reinforcement into the concrete core; namely, RCFT structures. According to the experimental study results on RCFT structures (Hua et al., 2005;. Wang et al., 2002), the bearing capacity, ductility, deformation, shear-resistance and anti-seismic capacity of RCFT structures is improved compared to those of CFT. RCFT not only inherits the advantages of CFT, but also makes up for the weak points of CFT,. 21.

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